Thermal insulation products for use with non-planar objects

ABSTRACT

High-efficiency thermal insulation products and methods for use thereof for insulating cylindrically-shaped and other non-planar objects such as pipes, tanks, and the like. One method includes heating a substantially gas-tight enclosure to render the gas-tight enclosure pliable, wrapping the inner surface of the gas-tight enclosure about at least a portion of a non-planar surface, and cooling the gas-tight enclosure to render the gas-tight enclosure substantially unpliable about the non-planar surface. The gas-tight enclosure may include a sealed interior portion having a pressure that is not greater than about 500 mbar at a temperature of about 20° C. before the heating step and/or after the cooling step. A ratio of a thickness of the gas-tight enclosure to a radius of curvature of the portion of the non-planar surface may be at least about 1 to 8.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority as a divisional application of U.S.patent application Ser. No. 14/154,760, filed on Jan. 14, 2014 now U.S.Pat No. 9,133,973, which claims priority as a continuation-in-part ofU.S. patent application Ser. No. 13/741,194, filed on Jan. 14, 2013 nowU.S. Pat No. 9,726,438, which claims the priority benefit of: U.S. Pat.App. Ser. No. 61/799,173, filed on Mar. 15, 2013; U.S. Pat. App. Ser.No. 61/799,752, filed on Mar. 15, 2013; and U.S. Pat. App. Ser. No.61/799,590, filed on Mar. 15, 2013. All the contents of theaforementioned applications are incorporated herein by reference intheir entirety as if set forth in full.

This application also incorporates by reference the followingnon-provisional patent applications filed on Jan. 14, 2014: U.S. patentapplication Ser. No. 14/154,704 now U.S. Pat No. 9,849,405 and U.S.patent application Ser. No. 14/154,806 now U.S. Pat No. 9,598,857.

BACKGROUND

1. Field of the Invention

The present invention generally relates to high-efficiency insulationproducts (e.g., panels) and, more particularly, to high-efficiencyinsulation products that may be applied about cylindrically-shaped orother non-planar objects (e.g., pipes, tanks, etc.) to limit heattransfer into and out of the non-planar objects.

2. Relevant Background

Thermal insulation generally refers to a porous material with aninherently low thermal conductivity serving to protect the system ofinterest from heat flow into or out of its surroundings. The use ofthermal insulation is prevalent in society ranging from use in domesticrefrigerators (e.g., for reduced energy consumption or additionalinternal volume), in shipping containers containing ice or dry ice usedfor drugs or food (e.g., to extend the lifetime of the shipment), in thetiles on the space shuttle (e.g., used to protect the shuttle from theheat of reentry into the atmosphere), and/or the like. Most thermalinsulation products used today are either fibrous materials, such asfiberglass, mineral wool and asbestos, or polymer foams, such asexpanded polystyrene, polyurethane, foamed polyethylene and foamedpolypropylene. Use of fibrous materials may be undesirable in manyinstances due to problems related to health and safety. Use of polymerfoams may be undesirable due to their flammability, lack ofrecyclability and release of environmentally unfriendly gases, such asfluorocarbons or hydrocarbons during manufacture. In addition, thethermal performance of both fibrous materials and polymer foam materialsare on the same order as or greater than stagnant air (e.g., about 0.026W/mK at ambient temperature). Because of increased concern with respectto energy efficiency and the environment, there has been much interestin the development of new classes of thermal insulation that have athermal conductivity much less than that of air, such as aerogels, inertgas-filled panels and vacuum insulation panels.

For thermal insulation, a key measure of performance is the thermalconductivity of the material. More specifically, lower thermalconductivity means lower heat flow through the insulation for a giventemperature difference. In the absence of convection, heat transferthrough insulation occurs due to the sum of three components: solidphase conduction, gas phase conduction and radiation. Solid phaseconduction may be minimized by using a low density material (e.g., amaterial comprising a high volume fraction of pores). Most insulation isbetween, for instance, 80 and 98% porous. It is also advantageous to usea solid material that has a low inherent thermal conductivity (e.g.,plastics and some ceramics/glasses are better than metals).

The relative importance of radiation depends upon the temperature rangeof interest and becomes a more prevalent component as the temperature isincreased above ambient and/or the magnitude of the other heat transfermodes is minimized. Materials with high infrared (IR) extinctioncoefficients due to absorption (e.g., IR opacifiers such as carbonblack, iron oxide, etc.) or scattering (e.g., titania) are often addedto high performance insulation to limit radiative heat transfer.

With control of radiation, suppression of free convection, use of lowthermal conductivity materials and a highly porous solid matrix, thethermal conductivity of the insulation approaches that of the gascontained within the pores of the insulation. There are a number ofmethods for lowering gas phase conduction in insulation. One method todo so is to trap gases in the pores that have lower thermal conductivitythan that of air, such as argon, carbon dioxide, xenon and krypton.Depending upon the gas employed, the thermal conductivity of insulationfilled with an inert gas can range from, for instance, 0.009 to 0.018W/mK. However, the insulation must be packaged such that the filler gasdoes not leak from the pores and also so that atmospheric gases (e.g.,nitrogen, oxygen) do not penetrate the insulation.

Another method for controlling or lowering gas phase conduction is toemploy the Knudsen effect. Generally, gas phase conductivity within theinsulation may be dramatically reduced when the mean free path of thegas approaches the pore size of the insulation. In fact, gas phaseconductivity may approach zero (so that the total effective thermalconductivity is the sum of only radiation and solid phase conduction)when the mean free path of the gas is much larger than the pore size.For instance, the mean free paths of the components of air areapproximately 60 nanometers at ambient temperature and pressure, whilethe pore/cell size of polymer foams and fibrous materials is typicallygreater than 10 microns.

There are at least two approaches that can employ the Knudsen effect tolower gas phase conduction. A first approach is to encapsulate theinsulation within a barrier material and partially evacuate the gas inthe insulation (i.e., use a vacuum pump to evacuate the insulativematerial). This increases the mean free path of the gas by lowering thegas density, which lowers gas phase conduction. Materials employing suchgas evacuation techniques can achieve a thermal conductivity of lessthan 0.002 W/mK at ambient temperatures, which is an order of magnitudeimprovement over conventional insulation.

The advantages of utilizing a vacuum with an insulative material havebeen known for many years and are the basis of vacuum Dewars that areused with cryogenic liquids and for storing hot or cold beverages orother products. For example, U.S. Pat. No. 1,071,817 by Stanleydiscloses a vacuum bottle or Dewar, where a jar is sealed inside anotherjar with a deep vacuum maintained in the annular space with the two jarsbeing joined at the jar mouth. Such an approach minimizes joining andthermal bridging problems, but most insulation applications require manydifferent shapes that cannot be met by a Dewar.

Another approach is to use a material with very small pores and lowdensity. One such class of materials is nanoporous silica, also known assilica aerogels, which generally have small pores (e.g., <100 nm), a lowdensity, and exhibit a total thermal conductivity at ambient pressurethat is lower than that of the gas contained within the pores. It isknown to use nanoporous silica in conjunction with a vacuum to create avacuum insulation panel (VIP). U.S. Pat. No. 4,159,359 byPelloux-Gervais discloses the use of compacted silica powders, such asprecipitated, fumed, pyrogenic, or aerogels, contained in plasticbarriers, which are subsequently evacuated and then sealed.

SUMMARY

It is often desirable to limit heat transfer into or out of a system ofinterest having non-planar or curved outer walls rather than necessarilyplanar outer surfaces. More specifically, VIPs can sometimes be appliedaround curved surfaces such as pipes, cylindrical tanks, and the like tolimit heat flow through the outer walls and maintain a desired operatingtemperature range within the outer walls. For instance, sleeve-likeinsulators are sometimes applied about cryogenic pipelines and becomeevacuated (e.g., due to condensing of CO₂ contained within theinsulators) when exposed to cryogenic temperatures (e.g., cyropumping).However, these types of sleeve-like insulators are typically onlyconfigured for use with a particular diameter of pipe and often must beapplied to the pipe before installation of the pipe into the particularsystem of interest. Furthermore, these insulators are ineffective unlessthe fluid temperature contained within the pipelines is low enough tocondense or cause direct solid-vapor deposition of the CO₂ or otherfluid contained within the sleeve to evacuate the inside of the sleeve.

While VIPs can sometimes be formed into non-planar shapes duringmanufacture, the VIPs are then set in the particular non-planar shapethroughout their lifespan and are thus only configurable to a particularshape and/or contour of a surface to be insulated. As a still furtherexample, some VIPs can be bent around curved surfaces in an attempt tolimit heat transfer through the curved surface. However, bending a VIPabout a curved surface (e.g., especially those surfaces of reduced radiiof curvature or bending radii) can result in crimping of one of thebarrier walls of the VIP into the other thereby forming a “cold short”where the walls contact each other; in other situations, bending a VIPcan even result in rupture of the VIP due to the inelastic nature of thebarrier materials. To limit the likelihood of rupture when bending a VIParound a curved surface, the VIP is often required to be of minimalthickness which necessarily limits its thermal performance.

In view of the foregoing, the present invention is directed tohigh-efficiency insulation products (e.g., panels, sections, etc., ofany appropriate shape and dimensions) and systems, methods ofmanufacture thereof, methods of use thereof for insulatingcylindrically-shaped or other non-planar walls (e.g., pipes, tanks,etc.) to limit heat transfer into and out of the non-planar walls. Aswill be discussed herein, the disclosed utilities (e.g., products,apparatuses, systems, methods, processes, etc.) allow for significantincreases in thermal performance, increases in the range of operatingconditions in which the disclosed utilities can be utilized (e.g., inrelation to the types of curved surfaces, operating temperatures of thesystems of interest, etc.), reductions in costs (e.g., electricitycosts), and the like, in relation to current products and methods forinsulating non-planar surfaces.

In one arrangement, the disclosed thermal insulation products can beevacuated free of the use of mechanical vacuum pumps thus allowing forprocessing and sealing (e.g., encapsulation) to occur at ambientpressures. Eliminating or at least limiting the use of energy-intensivevacuum pumps to evacuate the disclosed products allows for theelimination or at least reduction in the volume or amount of at leastsome of the components making up the nanoporous core (e.g., such as thefibers typically present in current VIPs to maintain the structuralintegrity of the VIPs during the mechanical evacuation process), panelshrinkage during such mechanical evacuation thus allowing for improved(e.g., less variable) panel dimensions, reduced energy consumption,reduced overall process steps, reduced capital investment, and the like.As will also be discussed below, the present thermal insulation productproduction processes at least substantially eliminate the need fordrying of the core material (e.g., nanoporous silica) before sealing ofthe same within the outer gas-impermeable barrier or envelope which alsoreduces energy consumption, overall process steps, capital investment,product variability, and the like.

For purposes of this disclosure, “ambient” refers to the conditions(e.g., temperature and/or pressure) of the general environment withinwhich the thermal insulation products according to the embodimentsdisclosed herein are produced. For instance, at about sea level, theproduction of the thermal insulation products disclosed herein wouldoccur at an ambient pressure of about 1013 mbar, while at an elevatedlocation such as Albuquerque, NM (e.g., elevation of about 5355′), theproduction would occur at an ambient pressure of about 800 mbar.Furthermore, the ambient temperature will be assumed to be a normalinside air temperature (e.g., between about 12-38° C., such as about 21°C.) where the disclosed thermal insulation products are produced.

In one aspect, a system includes a cylindrical wall (e.g., pipe, tank)having an outside surface and a thermal insulation product disposedabout the cylindrical wall. The thermal insulation product includes asubstantially gas-impermeable envelope (e.g., gas-tight enclosure suchas a metallic and/or polymeric film) having inner and outer opposingsurfaces and a thickness between the inner and outer opposing surfaces,a sealed interior portion within the gas-impermeable envelope betweenthe inner and outer opposing surfaces and having a pressure of notgreater than about 500 mbar at a temperature of at least about 20° C.,and a support material (e.g., a nanoporous core) including a particulateblend (e.g., a fine powder such as silica powder, aerogel powder, etc.)within the interior portion. The inner surface of the gas-impermeableenvelope abuts (e.g., adjacent, directly contacts, etc.) the outsidesurface of the cylindrical wall along at least a portion of (e.g., some,most or a substantial entirety of) a circumference of the cylindricalwall. Furthermore, a ratio of the thickness of the substantiallygas-impermeable envelope to an outer radius of the portion of thecylindrical wall is at least about 1 to 8.

For instance, the ratio of the thickness of the substantiallygas-impermeable envelope to the outer radius of the portion of thecylindrical wall may be at least about 1 to 4,such as at least about 1to 2. As another example, the thickness of the gas-impermeable envelopemay be at least about 2 mm, such as at least about 10 mm, or at leastabout 20 mm. As another example, the thickness of the gas-impermeableenvelope may be not greater than about 100 mm, such as not greater thanabout 80 mm, or not greater than about 60 mm. As a still furtherexample, the radius of curvature may be at least about 3 mm, such as atleast about 6 mm, or at least about 10 mm. In one variation, an innersurface of a second thermal insulation product (e.g., elastomeric foam,fiberglass, etc.) may be disposed about the first thermal insulationproduct so as to abut the outer surface of the first thermal insulationproduct. In another variation, the pressure within the gas-impermeableenvelope may be not greater than about 250 mbar at a temperature of atleast about 20° C., such as not greater than about 100 mbar, or notgreater than about 20 mbar, or not greater than about 5 mbar.

In some arrangements, the thermal insulation product may be manufacturedinto a desired non-planar shape (e.g., so that the inner surface of thethermal insulation product comprises a curvature or contour generallymatching that of an outer surface of a non-planar or cylindricalsurface). For instance, a substantially gas-tight enclosure having firstand second opposing surfaces and a thickness between the first andsecond opposing surfaces may have a sealed interior portion within thegas-tight enclosure between the first and second opposing surfaceshaving a pressure not greater than about 500 mbar at a temperature of atleast about 20° C. and a support material therewithin, where a ratio ofthe thickness to a radius of curvature of the first surface is at leastabout 1 to 8, such as at least about 1 to 4.

In other arrangements, the thermal insulation product may bemanufactured in a planar shape (e.g., a panel) and the product may besubsequently appropriately formed into a desired non-planar shape (e.g.,one or multiple times). For instance, one method disclosed hereinincludes heating a substantially gas-tight enclosure having a sealedinterior portion to render the gas-tight enclosure substantiallypliable, wrapping an inner surface of the gas-tight enclosure about atleast a portion of a non-planar surface, and cooling the gas-tightenclosure to render the gas-tight enclosure substantially unpliable. Aratio of the thickness to a radius of curvature of the portion of thenon-planar surface may be at least about 1 to 8, such as at least about1 to 4.

Advantageously, the thermal insulation product may be conformed tonon-planar surfaces of numerous different sizes, contours (e.g., radiiof curvature) and dimensions; is not necessarily limited to reducedthicknesses (e.g., less than 2 mm) to conform to reduced radii ofcurvature; and does not necessarily require cryogenic conditions tomaintain a substantially evacuated state within the gas-impermeableenvelope. In one embodiment, the pressure within the interior portion ofthe gas-tight enclosure may be not greater than about 500 mbar after thecooling step even when a fluid disposed within the non-planar surface(e.g., within a pipe or tank) is at a temperature of at least about 80 °C., such as at least about 140 ° C., or at least about 200 ° C. Forinstance, the cooling step may include cooling the gas-tight enclosuredown to a substantially ambient temperature. In another embodiment, thegas-tight enclosure may be secured to the non-planar surface (e.g., suchas via adhesives and/or in other appropriate manners).

In one arrangement, the thermal insulation product may be manufacturedby way of sealing the support material and at least one vapor (e.g.,steam) within the interior portion of the gas-impermeable envelope wherethe interior portion of the gas-impermeable envelope is at a firstpressure during the sealing step, and then condensing at least a portionof the gas after the sealing step. Condensing at least a portion of thegas after the sealing step reduces the pressure within the interiorportion of the gas-impermeable envelope from the first pressure down toa second pressure (e.g., a substantially evacuated pressure similar toor better than that of current VIPs) free of many of the additionalprocess steps, capital investment, energy consumption and the likeassociated with having to manually evacuate (e.g., with a mechanicalpump) the interior of the envelope, sufficiently drying the supportmaterial before sealing, and the like.

Generally, the reduction in pressure results from the principle that aquantity of molecules will take up less volume in an impermeablecontainer (e.g., envelope) in a liquid state compared to the samequantity of molecules in a gaseous state (e.g., as a vapor). Forinstance, the vapor can be initially sealed within the gas-impermeableenvelope at a temperature that is both above a boiling point (e.g.,condensation point) of the substance making up the vapor as well asabove ambient temperatures. The vapor can then be cooled down to atemperature below the condensation/boiling point of the substance makingup the vapor, such as down to or above an ambient temperature, tocondense at least a portion of the vapor and thereby create a lowerpressure state or an at least partial vacuum within the gas-impermeableenvelope. For purposes of this discussion, all references to the boilingor boiling point of a particular substance or compound making up thevapor or liquid will be in the context of atmospheric pressure.

As the vapor is initially sealed at an elevated temperature (i.e., withrespective to an ambient temperature) and then cooled down to ambient toat least partially condense the vapor and thereby create and maintainthe lower pressure state within the gas-impermeable envelope, thegas-impermeable envelope advantageously need not necessarily bemaintained in contact with a cold source (e.g., such as a cryogenic tankor pipeline) to maintain the low pressure state within thegas-impermeable envelope in use. Furthermore, the first/initial pressurewithin the sealed gas-impermeable envelope (i.e., before the condensingstep) can be at or slightly above ambient pressure which eliminates orat least limits the need for creating a vacuum within thegas-impermeable envelope with convention mechanical pumping mechanismsduring manufacture.

Many vapors and/or vaporous mixtures are envisioned that may be sealedwithin the gas-impermeable enclosure and condensed (e.g., via reducingan elevated temperature of the vapor(s) down to a temperature at orabove ambient temperatures) to enact the disclosed pressure reductionwithin the gas-impermeable envelope (which correspondingly reduces thegas phase conduction within the envelope). In one arrangement, thevapor(s) may have a thermal conductivity lower than that ofnitrogen/air. Additionally or alternatively, the vapor(s) may be a vaporor vapors whose pressure within the gas-impermeable envelope drops by alarger amount than would air for a common reduction in temperature. Inthis regard, the vapor/vaporous mixture may be considered an “airreplacement” that displaces at least some of the air that wouldotherwise be present within the interior portion of the gas-impermeableenclosure.

For instance, sealing air within the gas-impermeable envelope at sealevel and at a temperature of about 100° C. and then cooling thegas-impermeable envelope down to a temperature of about 20° C. wouldcause the pressure within the gas-impermeable envelope to drop fromabout 1000 millibars (mbar) down to about 785 mbar. In contrast, and inaccordance with one embodiment of the present disclosure, sealing steam(i.e., vaporous water or H₂O) within the gas-impermeable envelope at atemperature of at least about 100° C. and then cooling thegas-impermeable envelope down to a temperature of about 20° C. willcause the pressure within the gas-impermeable envelope to drop fromabout 1000 mbar down to a pressure below 785 mbar, such as down to about20 mbar. In addition to or other than steam, vapors that may be sealedwithin the disclosed gas-impermeable envelope include, but are notlimited to, paraffins such as n-pentane, chlorohydrocarbons such ascarbon tetrachloride, CFCs, HCFCs, oxygenated organics such as acetoneand ethylene glycol, and a wide range of vapors. For instance, thevapors may be selected based on one or more properties orcharacteristics of the vapors such as thermal conductivity at one ormore particular temperatures, mean free path at a particular pressureand/or temperature, vapor pressure difference between two particulartemperatures, and/or the like.

In one arrangement, two or more different vapors may be sealed withinthe gas-impermeable envelope to impart any desired properties orcharacteristics to the thermal insulation product to be formed (e.g.,properties/characteristics not achievable through use of a singlevapor). For instance, the vapor pressure/temperature curve for avaporous mixture of two or more vapors sealed within the gas-impermeableenvelope can be specifically tailored to a desired end-use of theproduct by appropriately selecting the two or more vapors (e.g., so thatthe resulting vapor pressure within the product achieves a desired levelfor a particular use temperature).

In some situations, the thermal insulation products and methodsdisclosed herein may be used to provide insulation in hot temperatureapplications. That is, the disclosed thermal insulation products may beused to maintain an interior of an enclosure (e.g., of a non-planarobject such as processing piping, tank, vat, etc. containing anyappropriate fluid, solid, etc.) at a particular hot temperature, such asabove about 100° C. As an example, the specific vapor(s) included withinthe interior portion of the gas-impermeable envelope may be chosen sothat the boiling point is above the temperature of the particularenvironment and context in which the finished thermal insulation productis to be used. For instance, for relatively hot applications (e.g.,process piping through which a fluid flows or is contained, ovens,environmental test chambers, aerospace, exhaust gases, etc., such as attemperatures of greater than 100° C., greater than 150° C., etc.), itmay be desirable to utilize a vapor that has a boiling point higher thanthat of water (i.e., higher than 100° C.) to allow the vapor to be inequilibrium with a condensed state (e.g., the liquid).

For instance, the vapor (e.g., or vaporous mixture) may be selected sothat its boiling point is higher than the temperature of a particularcontemplated hot temperature application. In one arrangement, the vapormay be in the form of an organic compound (e.g., alcohol, such as atleast on diol) and/or a silicone-based compound (e.g., dimethylpolysiloxane compound). In another arrangement, the vapor may have aboiling point that is at least about 150° C. at about 1000 mbar ofpressure. In this arrangement, for example, the interior portion of thegas-impermeable envelope may have a temperature that is at least about125° C. after the condensing step (e.g., imparted by a particular hottemperature application). In another arrangement, the vapor may have aboiling point that is at least about 200° C. at about 1000 mbar ofpressure. In this arrangement, for example, the interior portion of thegas-impermeable envelope may have a temperature that is at least about125° C. after the condensing step, such as at least about 150° C. afterthe condensing step, or at least about 175° C. after the condensing step(e.g., imparted by a particular hot temperature application). In afurther arrangement, the vapor may have a maximum molecular weight ofnot greater than about 200,such as not greater than about 150.

In addition to the innate thermal conductivity and density of the vaporwithin the gas-impermeable envelope, the Knudsen effect can also beemployed to reduce or otherwise control gas phase conduction within thegas-impermeable envelope. That is, increasing the mean free path of thevapor (which can be controlled by selecting one or more particularvapors and/or reducing the pressure/density of the vapor(s)) to beapproximately equal to or greater than an average pore size of thesupport material within the gas-impermeable envelope can greatly reduceor even substantially eliminate gas phase conduction within theenvelope. In this regard, at least a portion of the vapor within theinterior of the sealed gas-impermeable envelope can be condensed so thatthe remaining vapor within the interior of the sealed gas-impermeableenvelope has a mean free path about equal to or larger than an averagepore size of the support material.

In one arrangement, the support material may be in the form of anadsorbent material (e.g., powder(s), particulate(s), blend(s), and/orthe like) having a relatively low thermal conductivity (i.e., lowsolid-phase conductivity, such as not greater than 0.005 W/mK), poressized to facilitate the Knudsen effect (e.g., nanoporous materials), andbeing relatively inexpensive and/or lightweight (e.g., having a densityof not greater than about 250 g/l). For instance, the support materialmay be a particular blend comprising a fine (e.g., nanoporous) powder(e.g., fumed silica and silica aerogels), available from, for example,Evonik, Essen, Germany. In one embodiment, the support material mayinclude at least about 60 wt % of the fine powder. In anotherembodiment, the support material may include about 100 wt % of the finepowder.

In some arrangements, the support material may additionally include anyappropriate quantity and/or type of an IR opacifier/radiation absorbentmaterial (e.g., titania, silicon carbide, carbon black, and/or the like)for purposes of limiting radiative heat transfer through the supportmaterial. In one embodiment, the support material includes at leastabout 5 wt % of the IR opacifier. In another embodiment, the supportmaterial includes not greater than about 25 wt % of the IR opacifier.

Additionally or alternatively, the support material may also include oneor more lightweight fibers to enhance the structural integrity of theresulting thermal insulation product, such as polyethylene fibers,polyester fibers, other plastic fibers, carbon fibers, glass fibers,metal fibers and/or other fibers. In one embodiment, the supportmaterial may include not greater than about 0.1 wt % of fibrousmaterials.

Additionally or alternatively, the support material may also include anyappropriate structural filler (e.g., perlite) to enhance the structuralintegrity of the resulting thermal insulation product. In oneembodiment, the support material may include at least about 10 wt % ofthe structural filler. In another embodiment, the support material mayinclude not greater than about 70 wt % of structural filler.

Additionally or alternatively, the support material may also include anyappropriate getter (e.g., oxygen/nitrogen getter) such as iron, barium,lithium, zeolites, etc. to maintain the low pressure state within thegas-impermeable envelope, such as by combining with the gas moleculeschemically and/or by adsorption. In one embodiment, the support materialincludes at least about 0.01 wt % of a getter. In another embodiment,the support material includes not greater than about 1 wt % of a getter.

In the event that the fine powder (e.g., fumed silica) is combined withone or more additional components to form the support material, all ofsuch components may be mixed in any appropriate manner to create asubstantially homogenous composition. In one approach, thepower/particular adsorbent material may be mixed with an IR opacifier tocreate a first mixture. This first mixture may then be mixed with afibrous material and/or structural filler material to create the supportmaterial. In another approach, the powder/particulate adsorbentmaterial, IR opacifier, fibrous material and/or structural fillermaterial may be mixed simultaneously to create the support material.

In one arrangement, the support material may have a total porosity of atleast about 80%. In another embodiment, the support material may have atotal porosity of not greater than about 98%.

In one arrangement, the support material may have an average pore sizeof at least about 20 nanometers. In another embodiment, the supportmaterial may have an average pore size of not greater than about 2,000nanometers, such as not greater than about 500 nanometers to facilitatethe Knudsen effect.

In one arrangement, the support material may have a surface area of atleast about 50 m²/g. In another embodiment, the support material mayhave a surface area of not greater than about 1,500 m²/g.

As noted, the support material is sealed along with a vapor within aninterior portion of a substantially gas-impermeable envelope before thevapor is condensed to reduce the pressure within the interior portion.Any appropriate or suitable material may be utilized to form thegas-impermeable envelope such as plastic laminates, metallized plastics,metals, metal-foils (e.g., stainless steel for higher temperatures), andelectroplated metals, to name a few. In one arrangement, thegas-impermeable envelope may be made of an Ethylene Vinyl Alcohol (EVOH)barrier film, a coextruded polyethylene (PE)/EVOH barrier film, ametalized EVOH barrier film, and/or the like. The type and shape of thegas-impermeable envelope may be generally related to the application inwhich the thermal insulation product is to be utilized. In shippingapplications, for example, it may be desirable to utilize thin,panel-shaped enclosures made of a metallized plastic (e.g., metallizedPolyethylene terephthalate (PET)). In one embodiment, thegas-impermeable envelope may include a thickness of at least about 10microns, such as at least about 25 microns. In another embodiment, thegas-impermeable envelope may include a thickness of not greater thanabout 300 microns, such as not greater than about 200 microns.

The sealing step may be accomplished in any known manner suitable to thetype of gas-impermeable envelope employed. For example, heat sealing maybe used for plastic laminate enclosures and welding for metalenclosures. In relation to the former and in one embodiment, a flowwrapping machine may be utilized to seal the gas-impermeable enclosureabout the support material and gas/gas mixture.

Furthermore, the condensing step may be accomplished in any appropriatemanner, such as by cooling the vapor to a temperature below a boilingpoint of the vapor after the sealing step. In one arrangement, thegas-impermeable envelope may include spaced apart first and secondsidewalls, and the cooling step may include respectively contacting thefirst and second sidewalls with first and second surfaces havingtemperatures below the boiling point of the vapor. For instance, each ofthe first and second surfaces may form parts of respective first andsecond molding members of a mold and collectively define a mold cavity.In this case, the first and second molding surfaces may be broughttogether over the first and second sidewalls of the envelope underslight pressure to cool the envelope and the vapor thereinside tosimultaneously condense the vapor as well as form a thermal insulationproduct from the envelope into a desired shape (e.g., a relativelyplanar, rectangular-shaped panel; a non-planar shape such as an L-shapedor U-shaped panel; and/or the like).

In another arrangement, an outer surface of the gas-impermeable envelopemay be contacted with a cooling liquid having a temperature below theboiling point of the vapor. For instance, a cooling liquid such as wateror the like may be sprayed or otherwise applied over the outer surfaceof the gas-impermeable envelope to cool and thereby condense at least aportion of the vapor inside the envelope. In a further arrangement, thegas-impermeable envelope (and the vapor and support material therein)may be passively cooled under a substantially ambient temperature downto the ambient temperature to condense at least a portion of the gasinside the envelope.

In one variation, the support material and vapor may be sealed (e.g., atan ambient pressure) within a gas/vapor-permeable or porous enclosure(e.g., that is still liquid impermeable), where the gas-permeableenclosure (with the support material and vapor disposed thereinside) issealed (e.g., again, at the same ambient pressure) within the interiorportion of the gas-impermeable envelope before the vapor mixture iscondensed (e.g., via cooling the gas-impermeable envelope down toambient temperature or some temperature above ambient temperature) tolower the pressure within the gas-impermeable envelope. Morespecifically, it has been found that doing so provides a number ofbenefits such as facilitating handling of the support material andvapor, facilitating sealing of the gas-impermeable envelope (e.g., bylimiting the degree to which the support material becomes disposedbetween the two surfaces that are to be sealed), and/or the like. Forinstance, the gas-permeable enclosure may be similar to those used fordesiccant bags, fiberglass bundling, etc.

In one arrangement, the support material and vapor mixture may first bedisposed and sealed within the gas-permeable enclosure, and then thesealed gas-permeable enclosure may be sealed within the gas-impermeableenvelope (e.g., via encapsulating the gas-impermeable envelope about thesealed, gas-permeable enclosure). For instance, the support material andvapor may be simultaneously injected into the gas-permeable enclosure.As another example, the support material may be injected first and thevapor second, or vice versa. In one variation, the support material maybe injected or otherwise disposed into the gas-permeable enclosure, aliquid (e.g., water) may be applied over the support material within thegas-permeable enclosure (e.g., via spraying the liquid over the supportmaterial), and the support material and liquid may then be heated abovethe boiling point of the liquid to convert at least some of the liquidinto a gas/gas mixture and drive some or all air out of thegas-permeable enclosure.

After sealing the gas-permeable enclosure (where the sealing may beperformed before or after heating the support material and liquid abovethe boiling point of the liquid), the sealed gas-permeable enclosure(which has the support material and vapor thereinside) may be sealedwithin the gas-impermeable envelope before eventually being cooled tore-condense the vapor within the gas-permeable and gas-impermeableenclosures back into the liquid state and thereby reduce the pressurewithin the resulting thermal insulation product. In one embodiment, andregardless of how the support material and vapor are disposed within theinterior portion of the gas-impermeable envelope, a desiccant may, justbefore sealing of the gas-impermeable envelope, be disposed between thegas-impermeable envelope and the gas-permeable enclosure to furtherreduce the pressure within the sealed gas-impermeable envelope (e.g., bysuch as adsorbing or absorbing the condensed liquid, chemically bondingwith the molecules of the condensed liquid, and/or the like).

In addition to the above-discussed advantages (i.e., no or little needfor mechanical vacuum pumps, drying of the support material, etc.), thethermal insulation products produced by the processes disclosed hereincan also be designed to have a reduced overall (e.g., bulk) densitycompared to current VIPs (e.g., 10-20% lower). For instance and incontrast to current VIPs, a smaller quantity of or even no fibrousmaterials needs to be utilized within the support material of thepresent thermal insulation products because mechanical pumpingmechanisms need not be used to draw the vacuum within the presentthermal insulation products. Stated otherwise, the extra structuralintegrity provided to the products by such fibrous materials may not benecessary as mechanical pumping mechanisms need not be used, as thepresent thermal insulation products need not be forcefully pressed toform the products into a desired shape, and the like.

In another regard, a smaller quantity of or even no IRopacifiers/radiation absorbent materials needs to be utilized within thesupport material of the present thermal insulation products as at leastsome of the vapors that may be sealed along with the support materialwithin the gas-impermeable enclosure serve to absorb IR radiation andthereby limit radiative heat transfer through the thermal insulationproduct. For instance, when silica (e.g., nanoporous silica) is utilizedas the primary insulation material in the core of current VIPs, aradiation absorbent material (e.g., carbon black) is often added in anattempt to block the “IR absorption gaps” of the silica (i.e., those IRwavelengths not absorbable by the silica). However, when silica isutilized as the adsorbent powder/particulate of the support material ofthe present thermal insulation products disclosed herein, a radiationabsorbent material/IR opacifier need not necessarily be used in the caseof at least some vapors sealed with the silica within thegas-impermeable envelope. For instance, in the case of a vapor such assteam, the condensed steam (e.g., water) tends to naturally absorb thoseIR wavelengths not absorbable by the silica. In this regard, the numberof solid “components” making up the core of the present thermalinsulation products can be reduced (e.g., by eliminating/reducing thefibrous materials and/or IR opacifier) in relation to the core ofcurrent VIPs thereby resulting in lower bulk densities and simplifiedmanufacturing processes than those of current VIPs.

Any of the embodiments, arrangements, or the like discussed herein maybe used (either alone or in combination with other embodiments,arrangement, or the like) with any of the disclosed aspects. Merelyintroducing a feature in accordance with commonly accepted antecedentbasis practice does not limit the corresponding feature to the singular.Any failure to use phrases such as “at least one” does not limit thecorresponding feature to the singular. Use of the phrase “at leastgenerally,” “at least partially,” “substantially” or the like inrelation to a particular feature encompasses the correspondingcharacteristic and insubstantial variations thereof. Furthermore, areference of a feature in conjunction with the phrase “in oneembodiment” does not limit the use of the feature to a singleembodiment.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a thermal insulation product producedaccording to one embodiment disclosed herein.

FIG. 2a is a sectional view of the product of FIG. 1 before condensingof vapor within an interior of the product to reduce the pressure withinthe product.

FIG. 2b is a sectional view similar to that in FIG. 2a , but aftercondensing of at least some of the vapor within the interior of theproduct to reduce the pressure within the product.

FIG. 3 is a flow diagram illustrating a method of making the thermalinsulation product of FIG. 1, according to one embodiment.

FIG. 4a is a block diagram depicting an assembly line for making thethermal insulation product of FIG. 1.

FIG. 4b is a block diagram similar to that in FIG. 4a , but at anotherstage of the assembly line.

FIG. 4c is a block diagram similar to that in FIG. 4b , but at anotherstage of the assembly line.

FIG. 4d is a block diagram similar to that in FIG. 4c , but at anotherstage of the assembly line.

FIG. 4e is a block diagram similar to that in FIG. 4d , but at anotherstage of the assembly line.

FIG. 5 is a perspective view of the thermal insulation product of FIG. 1disposed about a non-planar outer surface.

FIG. 6 is a cross-sectional view through the line 6-6 of FIG. 5.

FIG. 7 is a flow diagram illustrating a method of applying the productof FIG. 1 about a non-planar surface.

DETAILED DESCRIPTION

The present disclosure is generally directed to highly efficient thermalinsulation products (e.g., panels, systems, methods of use, methods ofmanufacture, etc.) for use in insulating cylindrical or non-planarobjects such as pipes, tanks, and the like in manners that yieldsignificant cost/performance advantages over existing thermal insulationproducts. As will be discussed herein, the disclosed utilities allow forsignificant increases in thermal performance, increases in the range ofoperating conditions in which the disclosed utilities can be utilized,reductions in costs, and the like.

FIG. 1 presents a perspective view of one thermal insulation product 100(e.g., panel) that may be produced using the disclosed processes. Aswill be discussed in more detail in the discussion that follows, theproduct 100 may be utilized in numerous contexts where it is desired toprotect a system of interest having a non-planar surface from heat flowinto or out of its surroundings such as, but not limited to, piping,refrigeration equipment, storage tanks, and the like. As shown in FIG.1, the product 100 may be in the form of a generally “planar” memberhaving opposing first (e.g., top) and second (e.g., bottom) sides 104,108; a plurality of outer edge portions 112; and a plurality of cornerportions 116. A gas-impermeable envelope 120 (e.g., gas-tight enclosure)may form an outer boundary or layer of the product 100 and may haveportions sealed together in any appropriate manner (e.g., heat seal,adhesives, etc.) along a hermetically sealed portion 124 to seal aninsulative core thereinside as will be discussed in more detail below.

The gas-impermeable envelope 120 may be constructed from any appropriatematerial(s) such as plastic laminates, metallized plastics, metals,metal-foils, electroplated metals, and/or the like. Depending upon theparticular sealing process utilized, the gas-impermeable envelope 120may have a number of flaps such as first and second flaps 128, 132 thatmay, if desired, be folded and secured onto the first or second surfaces104, 108 of the product 100, at least partially cut off and removed,and/or the like. While the product 100 has been shown in FIG. 1 in theform of a generally planar panel, it is to be understood that theprocess disclosed herein may be utilized to make numerous other shapes,forms, sizes, contours, etc. of products 100 such as cylindrical-shaped,L-shaped, U-shaped, trapezoidal, square-shaped, angled edges, tongue ingroove edges, etc.

Turning now to FIG. 3, one embodiment of a method 200 for making thethermal insulation product 100 of FIG. 1 will now be discussed. Inconjunction with FIG. 3, reference will also be made to the sectionalviews of the product 100 presented in FIGS. 2a-2b as well as to thevarious stages of an assembly line 300 for producing the product 100presented in FIGS. 4a-4e .As shown in FIG. 3, the method 200 may includedisposing 204 a support material (e.g., core) and at least one vaporinto an interior portion of a gas-permeable enclosure (e.g., a porousbarrier such as that used for desiccant bags, fiberglass bundling, etc.)and then sealing 208 the support material and the at least one vaporwithin the interior portion of the gas-permeable enclosure (e.g., wherethe disposing 204 and sealing 208 substantially occur at an ambientpressure).

As discussed previously, the support material may be in the form of anadsorbent material (e.g., powder(s), particulate(s), blend(s), and/orthe like) having a relatively low thermal conductivity and pores sizedto facilitate the Knudsen effect (e.g., a fine powder such as fumedsilica, silica aerogels, etc.).

In some situations, one or more additives may be mixed in with theadsorbent material (and thereby form part of the support material) toadd one or more desired properties or qualities to the support material(and thereby the product 100 to be formed). For instance, one or more ofan IR opacifier (e.g., to limit radiative heat transfer through thesupport material), a lightweight fibrous material and/or a structuralfiller material (e.g., to enhance the structural integrity of theproduct 100 to be formed), a getter (e.g., to maintain the low pressureor evacuated state within the product 100 to be formed), and/or the likemay be included.

Furthermore, many vapors and/or vaporous mixtures are envisioned thatmay be disposed and sealed within the gas-permeable enclosure along withthe support material. The vapor may be a vapor with relatively lowthermal conductivity (e.g., lower than that of nitrogen/air) and/or maybe a vapor whose pressure drops by a desired amount along with aparticular reduction in temperature. As discussed herein, the vapor is,once sealed within a gas-impermeable envelope, cooled and condensed toreduce the pressure within the gas-impermeable envelope. In this regard,it may be advantageous to utilize vapors that have a boiling point abovethe operating temperatures of the environment in which the product 100to be formed is to be used so that the vapor remains condensed and theinside of the product 100 remains in the low pressure state during useof the product 100.

In addition to or other than steam (i.e., water), vapors that may besealed within the gas-permeable envelope include, but are not limitedto, paraffins such as n-pentane, chlorohydrocarbons such as carbontetrachloride, CFCs, HCFCs, oxygenated organics such as acetone andethylene glycol, and/or a wide range of vapors.

With reference to FIG. 2a , for instance, the support material(represented by the pattern of dots) and the at least one vapor(represented by the series of dashed lines and small circles) may bedisposed and sealed within an interior portion gas-permeable enclosure136 in any appropriate manner. Turning to FIG. 4a , for instance, thesupport material and at least one vapor may be initially maintained inrespective enclosures 308, 312 (e.g., tanks, pipes, vessels, etc.) aspart of an assembly line 300 that may be used to make the thermalinsulation products 100 disclosed herein. The enclosures 308, 312 may berespectively fluidly interconnected (e.g., via pipes, tubes, valves,etc.) to a chamber 316 to allow for the injection of the supportmaterial and at least one vapor into the chamber 316 and intermixingthereof. For example, a gas-permeable enclosure 136 may be moved alongthe assembly line 300 via a conveyor belt 304 or the like from oneposition as shown in FIG. 4a to another position as shown in FIG. 4b ,whereupon a mixture of the support material and the at least one vapormay be injected or otherwise appropriately disposed into thegas-permeable enclosure 136. The gas-permeable enclosure 136 may then besealed in any appropriate manner (e.g., such as by heat-sealing;adhesive; welding such as RF welding, solvent welding, or ultrasonicwelding; and/or the like) to contain the support material and at leastsome of (e.g., most of) the vapor within an interior portion thereof.

As discussed, the at least one vapor, once sealed within thegas-impermeable envelope 120, will be eventually cooled down to atemperature below a boiling point of the at least one vapor (e.g., at orabove an ambient temperature) to reduce the pressure within thegas-impermeable envelope 120 (as well as to eliminate or at least reducethe need to maintain the product 100 in contact with a cold source tomaintain the vapor in the condensed, low-pressure state). In thisregard, at least a portion of the assembly line 300, such as between andincluding the injection of the support material/gas mixture from thechamber 316 into the gas-permeable enclosure 136 up to the sealing ofthe sealed gas-permeable enclosure 136 within the gas-impermeableenvelope 120 (e.g., at station 320, discussed below), may be maintainedwithin any appropriate heating zone 328 that is configured to maintainthe at least one vapor at a temperature above its boiling point andlimit premature condensation of the vapor. For instance, the heatingzone 328 may be in the form of an enclosure made up of vinyl drapes,plastic walls, insulated walls, air curtains, and/or the like.

The support material and at least one vapor need not necessarily beinjected substantially simultaneously into the chamber 316 or even intothe interior portion of the gas-permeable enclosure 136. In onearrangement, the support material may be injected from the enclosure 308into the gas-permeable enclosure 136 (e.g., with or without passingthrough the chamber 316), and then the at least one vapor may beinjected from the enclosure 312 into the gas-permeable enclosure 136(e.g., also with or without passing through the chamber 316). In anotherarrangement, the support material may be injected or otherwise disposedinto the gas-permeable enclosure 136; a liquid (e.g., water) may beapplied over the support material (either before or after the supportmaterial is injected into the gas-permeable enclosure 136); and then thesupport material may be heated above the boiling point of the liquid toconvert at least some of the liquid into the at least one vapor andthereby drive some or all air out of the gas-permeable enclosure 136.Other manners of disposing and sealing the support material and at leastone vapor into the interior portion of the gas-permeable enclosure 136are also envisioned and included within the scope of the presentdisclosure.

Once the support material and at least one vapor have been sealed withinthe interior portion of the gas-permeable enclosure 136, the method 200of FIG. 3 may include sealing 212 the sealed gas-permeable enclosure 136within an interior portion of a gas-impermeable envelope (e.g., at apressure substantially equal to an ambient pressure). FIG. 2aillustrates the sealed gas-permeable enclosure 136 (having the supportmaterial and at least one vapor contained therein) being sealed withinan interior portion of the gas-impermeable envelope 120. At this point,for instance, the sealed interior portion of the gas-impermeableenvelope 120 may have about 1 gram of a liquid per liter of a totalvolume of the sealed interior portion of the gas-impermeable envelope120 (e.g., at a pressure substantially equal to ambient pressure).

In one arrangement, the sealed gas-permeable enclosure 136 may be movedalong the assembly line 300 by the conveyor belt 304 from the positionshown in FIG. 4b to that shown in FIG. 4c whereupon the sealedgas-permeable enclosure 136 may enter a gas-impermeable envelopeencapsulation/sealing station 320. For instance, the station 320 mayinclude at least a portion of a flow wrapping machine (e.g. includingspools/reels of the gas-impermeable envelope material, heat sealingequipment, etc., not shown) operable to wrap and seal the sealedgas-permeable enclosure 136 within the gas-impermeable envelope 120. Insome situations, any appropriate desiccant may be included within theinterior portion of the gas-impermeable envelope 120 but outside of thegas-permeable enclosure 136 for use in further reducing vapor pressurewithin the gas-impermeable envelope 120 upon cooling. In any event, thesealing 212 may occur with the at least one vapor being at a temperatureabove an ambient temperature (e.g., such as just outside of the heatedzone 328).

After the sealing 212, the method 200 of FIG. 3 may then include cooling216 the at least one vapor (which is contained along with the supportmaterial within the interior portion of the gas-impermeable envelope120) down to a temperature that is at least below the boiling point ofthe vapor (i.e., the substance(s) making up the vapor) to condense atleast a portion of the at least one vapor within the gas-impermeableenvelope 120 and thereby reduce the pressure within the gas-impermeableenvelope 120 from a first pressure upon the sealing 212 down to a secondpressure after the cooling 216 (e.g., free of energy intensive pumpingmechanisms). For instance, the at least one vapor may be cooled down toa temperature that is at or above an ambient temperature. In onearrangement, the difference between the first and second pressures maybe at least about 250 mbar, such as at least about 500 mbar at leastabout 700 mbar, or even at least about 900 mbar. In another arrangement,the reduced second pressure may be not greater than about 700 mbar, suchas not greater than about 500 mbar, not greater than about 300 mbar,such as not greater than about 100 mbar, or even not greater than about50 mbar. In a further arrangement, a time between the completion of thesealing 212 and the reduction of the first pressure to the secondpressure during the cooling 216 may be not greater than about 60minutes, such as not greater than about 10 minutes.

Turning now to FIG. 2b which illustrates a sectional view of the product100′ after the cooling 216, it can be seen how at least a portion of theat least one vapor (represented by the series of dashed lines and smallcircles in FIG. 2a ) has condensed into a liquid phase (represented bythe tighter series of dashed lines at the bottom of the interior portionof the gas-permeable enclosure 136 and gas-impermeable envelope 120 inFIG. 2b ). It can also be seen how any remaining vapor within theinterior portion of the gas-impermeable envelope 120 after the cooling216 is in a reduced density or expanded state in FIG. 2b compared to inFIG. 2a (e.g., note how the series of dashed lines and small circles isless dense in FIG. 2b compared to in FIG. 2a ). In other words, thecooling 216 converts at least a portion of the vapor into a liquid phaseso that the ratio of molecules within the interior portion of thegas-impermeable envelope 120 in the gas phase compared to those in theliquid phase decreases resulting in a decrease in pressure within thegas-impermeable envelope 120.

In one arrangement, the sealed interior portion may have at least about2 grams of a liquid per liter of a total volume of the sealed interiorportion of the gas-impermeable envelope 120 after the condensing/cooling216. For instance, the sealed interior portion may have at least about 3grams of a liquid per liter of a total volume of the sealed interiorportion of the gas-impermeable envelope 120 after the condensing/cooling216, such as at least about 4 grams of a liquid per liter. As anotherexample, the sealed interior portion may have not greater than about 7grams of a liquid per liter of a total volume of the sealed interiorportion of the gas-impermeable envelope 120 after the condensing/cooling216, such as not greater than about 6 grams of a liquid per liter, suchas not greater than about 5 grams of a liquid per liter.

As another example, the grams of liquid per liter of the total volume ofthe sealed interior portion of the gas-impermeable envelope 120 may beat least about two times greater (e.g., three times greater, four timesgreater, etc.) after the condensing/cooling 216 as compared to beforethe condensing/cooling 216 (e.g., such as just after the sealing 212).It is noted that the liquid has been illustrated as being concentratedat the bottom of the interior portion of the gas-impermeable envelope120 for purposes of facilitating the reader's understanding of thepresent disclosure and that the liquid may in reality be more disbursedwithin the support material throughout the interior portion of thegas-impermeable envelope 120.

For example, assume that the at least one vapor is steam and it issealed along with the support material within the interior portion ofthe gas-impermeable envelope 120 at a temperature of just over about100° C. In this regard, the pressure within the interior portion of thegas-impermeable envelope 120 may be about 1000 mbar (e.g., at or closeto ambient pressure). Upon cooling of the gas-impermeable envelope 120(and the steam and support material thereinside) down to a temperaturenear ambient temperature (e.g., down to about 20° C.), the pressurewithin the interior portion of the gas-impermeable envelope 120 may dropto only about 20 mbar. The pressure within the gas-impermeable envelope120 may thus advantageously substantially remain at the 20 mbar level(or other low pressure level) for uses of the resulting product 100 intemperatures substantially the same as the ambient temperature at whichthe product 100 was cooled 212.

For other vapors (e.g., n-pentane), the interior portion of thegas-impermeable envelope 120 may have a first temperature during thesealing step different (e.g., less) than that at which steam was sealed212 within the envelope 120, such as about 70° C., and/or a secondtemperature after the cooling step 216 different (e.g., greater) thanthat to which the envelope 120 was cooled 216, such as about 40° C. Ofcourse, further pressure reductions within the product 100 may result incold applications (e.g., refrigeration, shipping containers) in whichthe product 100 is disposed adjacent a cold source that causes furthercondensation of vapor remaining within the product 100. Additionalpressure reductions may result from the use of different types ofsupport material, pore sizes or overall porosities thereof, getters,and/or the like.

In any event, the sealed gas-impermeable envelope 120 may be moved alongthe assembly line 300 by the conveyor belt 304 from the position shownin FIG. 4c to that shown in FIG. 4d whereupon the sealed gas-permeableenclosure 120 may enter any appropriate cooling station 324 designed tocool the at least one vapor below its boiling point to condense at leasta portion of the vapor into a liquid phase. It is noted that before andat least partially during the time the sealed gas-impermeable envelope120 is cooling, it may be at least partially pliable (e.g., bendable byhand). In one arrangement, the cooling station 324 may include opposingplates or surfaces having temperatures below the boiling point of the atleast one vapor, where the opposing surfaces are configured torespectively contact the first and second sides 104, 108 (e.g., see FIG.2b ) of the product 100.

For instance, the first and second surfaces may lightly contact or pressthe first and second sides 104, 108 of the product 100 to simultaneouslycool the vapor below its boiling point (e.g., down to an ambienttemperature) and form the product 100 into more precise or exactdimensions, but need not exert any substantial amounts of pressureagainst the first and second sides 104, 108 of the product 100 (e.g.,because only minimal pressure may be required to maintain thermalcontact and guide shrinkage into a desired final shape). In oneembodiment, at least one of the opposing surfaces may have a depression,cavity, or the like, the shape of which is a desired shape of theproduct 100 to be formed (e.g., similar to a mold cavity). For instance,movement of at least one of the surfaces towards the other of thesurfaces may cause the product 100 to fill and expand in the cavityuntil the product 100 has assumed the shape of the cavity (e.g.,because, as discussed above the product 100 may be at least partiallypliable at least at the beginning of the cooling stage). As a result,the product 100 may be able to achieve increased dimensional stabilityand/or tighter tolerances. In another arrangement, the cooling station324 may be configured to spray a cooling liquid such as water or anotherliquid (e.g., having a temperature below the boiling point of the gas)over the outside of the product 100 to accelerate condensation of thevapor therewithin.

As discussed herein, the product may advantageously be used to insulatenumerous types of non-planar surfaces or cylindrically-shaped surfacessuch as pipe, storage tanks, and the like. In one arrangement, themethod 200 may include imparting or otherwise forming the product 100into any appropriate non-planar shape before or at least during thecooling step 216 (i.e., while the product 100 is still at leastpartially pliable and before the cooling step 216 has completed) so thatthe product is in the non-planar shape upon completion of the coolingstep 216 (i.e., so that the product is substantially rigid or unpliablein the non-planar shape after the cooling step 216). Numerous manners ofconforming and maintaining the product 100 in a desired non-planar orcylindrical shape while the cooling step 216 is occurring are envisionedand encompassed herein. In one arrangement, one of the first and secondsides 104, 108 (e.g., outer and inner surfaces, respectively) may beformed into a concave contour so that the product forms at least apartial cylinder (e.g., half cylinder or the like), where the other ofthe first and second sides 104, 108 would be correspondingly formed intoan at least partially convex contour. In another arrangement, theproduct 100 may be formed into a substantially full cylinder (e.g.,where the ends of the product substantially abut/face each other or areotherwise adjacent each other). In further arrangements, the product 100may be formed into other types of non-planar contours depending up oneor more particular end uses of the product 100.

Among other advantages, the product 100 may be configured to remain inan evacuated state (e.g., not greater than about 20 mbar at atemperature of about 20° C.) free of requiring cryogenic conditions tomaintain the evacuated state and while maintaining any appropriatenon-planar contour. Also in this regard, the product 100 may beconstructed to provide improved ratios of radii of curvature of theconcave surface of the product 100 (or of the non-planar surface overwhich the product is applied or disposed) to thickness of the product100 (i.e., the distance between the first and second sides 104, 108).More specifically, existing VIPs can sometimes be applied about curvedsurfaces having decreasing radii of curvature, but with the drawback ofdecreasing VIP thicknesses (i.e., due to the reduced thermal performancethat comes with decreasing VIP thickness).

In this regard, the ratio of the thickness of the product 100 to theradius of curvature of the concave surface of the product 100 (or of thenon-planar surface over which the product is applied or disposed) may beat least about 1 to 8,such as at least about 1 to 4 or at least about 1to 2.For instance, the radius of curvature of the concave surface of theproduct 100 (or of the non-planar surface) may be between about 3 mm to100 mm. In one arrangement, the radius of curvature of the concavesurface of the product 100 may be not greater than about 100 mm, such asnot greater than about 30 mm. As another example, the thickness of theproduct 100 may be at least about 2 mm, such as at least about 20 mm, orat least about 40 mm. As a further example, the thickness of the product100 may in other embodiments be not greater than about 100 mm, such asnot greater than about 80 mm, or not greater than about 60 mm.

In any event, the conveyor belt 304 may eventually move the finishedproduct 100 out of the cooling station 324 as shown in FIG. 4e whereuponthe product 100 may be ready for use, subjected to additional processing(e.g., securing or removal of the flaps 128, 132; quality control;etc.). In one arrangement, the finished product 100 may have a density(e.g., bulk density) of at least about 80 g/l. In another arrangement,the finished product 100 may have a density of not greater than about280 g/l. In one arrangement, the finished product 100 may have a thermalresistance of at least about 0.5 m²·K/W. In one arrangement, thefinished product 100 may have a thermal conductivity of not greater thanabout 0.010 W/mK at room temperature. It will be readily appreciatedthat many additions and/or deviations may be made from the specificembodiments disclosed in the specification without departing from thespirit and scope of the invention.

In one arrangement, the gas-impermeable envelope and vapor thereinsidemay be cooled 216 (e.g., by the cooling station 324 of FIG. 4d ) down toan initial temperature (e.g., about 60° C. in the case of the vaporbeing steam) at which the gas-impermeable envelope can at least maintaina desired shape so that a plurality of sealed gas-impermeable envelopescan be stacked or otherwise stored for future use. For instance, coolingsteam down to about 60° C. may cause the pressure within the sealedgas-impermeable envelope to drop from about 1000 mbar if produced nearsea level (e.g., upon initial sealing 212) down to about 150 mbar.Thereafter, continued ambient cooling of the sealed gas-impermeableenvelopes while stacked or otherwise stored (e.g., down to an ambienttemperature such as 21° C.) may cause further pressure reductions withinthe sealed gas-impermeable envelopes and thus finished products 100(e.g., down to about 20 mbar or the like).

As discussed previously, the thermal insulation products 100 disclosedherein may be manufactured and/or configured for use with non-planar orcurved surfaces (e.g., pipes, storage tanks, etc.) in manners thatprovide numerous advantages and efficiencies over existing insulationproducts. Turning now to FIGS. 5-6, respective perspective and sectionalviews of a product 100′ being disposed (e.g., wrapped, placed, etc.)about an outer non-planar surface 404 of a pipe 400 are presented (theprime (′) designation being used to signify that the product 100′ is inthe low pressure state of FIG. 2b ). More specifically, the second side108 (e.g., inner surface) of the product 100′ may be disposed against(e.g., directly, or at least abutting/adjacent) the outer surface 404 ofthe pipe 400 to provide resistance against heat flow into or out of afluid 600 (e.g., hot or cold water, hot or cold refrigerant, ammonia,cryogenic, etc.) flowing or contained within the pipe 400 (e.g., wherethe fluid 600 is at a temperature below the boiling point of the liquidwithin the product 100′). In one arrangement, the fluid 600 may be atcryogenic temperatures. In another arrangement, the fluid 600 may bebelow the freezing point of water, such as between about −50° C. and 0°C. In a further arrangement, the fluid 600 may be at or above asubstantially ambient temperature, such as at least about 50° C., or atleast about 100° C., or at least about 200° C.

For instance, the product 100′ may be slid onto an end of the pipe 400and then along the outer surface 404. Alternatively, the ends of theproduct 100′ (e.g., near seam 180 in FIG. 6) may be initially separatedto allow the second side 108 of the product 100′ to be fit about theouter surface 404 of the pipe 400 and then the ends may again be broughttogether. In one arrangement, any appropriate adhesive or the like maybe used to secure the second side 108 of the product 100′ to the outersurface 404 of the pipe and/or to secure the ends of the product 100′together at a seam 180. In another arrangement, more than one product100′ may be used to cover the outer non-planar surface 404 of the pipe400 (or other non-planar surface). For instance, first and secondproducts 100′ may be used, where each of the first and second products100′ covers about half of the outer non-planar surface 404 of the pipe400.

In a further arrangement, the product 100′ may be used in conjunctionwith one or more additional thermal insulation products such as a secondthermal insulation product 500 (e.g., fiberglass insulation, elastomericfoam, etc., where the second insulation product 500 is also configuredto be disposed in a non-planar/cylindrical shape) to provide ease ofinstallation of the product 100′, protection of the product 100′,increased thermal performance (e.g., decreased heat flow into or out ofthe pipe 400), and/or the like. For instance, the product 100′ may bedisposed about the outer surface 404 of the pipe 400 and then the secondinsulation product 500 may be disposed about the first side 104 of theproduct 100′. Alternatively, the first side 104 (e.g., outer surface) ofthe product 100′ may be initially disposed against an inner surface 508of the second insulation product (and/or secured thereto via adhesivesor the like).

Thereafter, the thermal insulation product 100′ and the second thermalinsulation product 500 may then be collectively disposed about the outersurface 404 of the pipe 400. For instance, the products 100′, 500 may beslid onto an end of the pipe 400 and then along the outer surface 404.Alternatively, the ends of the products 100′, 500 (e.g., near seams 180,580 in FIG. 6) may be initially separated to allow the second side 108of the product 100′ to be fit about the outer surface 404 of the pipe400 and then the ends may again be brought together. In one arrangement,a thickness between the outer and inner surface 504, 508 of the secondthermal insulation product 500 may be at least about 10 mm, such as atleast about 40 mm, or at least about 70 mm. In another arrangement, thethickness of the second thermal insulation product 500 may be notgreater than about 150 mm, such as not greater than about 120 mm, or notgreater than about 70 mm. In one specific arrangement in which the pipe400 has an outer diameter of about 25 mm, the thickness of the product100′ may be between about 3 mm to 13 mm while that of the second thermalinsulation product may be between about 6 mm to 75 mm.

In addition to reduced heat gain/loss with respect to the fluid 600contained within the pipe 400, the thermal insulation product 100′ alsoprovides increased levels of water vapor protection. In one variation,the gas-impermeable envelope 120 may be constructed of any appropriatemetalized plastic film or barrier (e.g., such as for hot sidetemperatures near ambient temperature). In another arrangement, thegas-impermeable envelope 120 may be constructed of stainless steel(e.g., such as for hot side temperatures over about 50° C., such as upto at least 400° C.).

As discussed previously, the product 100′ may be formed into anappropriate non-planar shape (e.g., such as that illustrated in FIG. 6)at the time of manufacture of the product 100′. In another arrangement,however, the product 100′ may be conformed about a non-planar surface(e.g., the outer surface 404 of the pipe 400) or otherwise formed into anon-planar shape sometime after the product was initially manufactured,such as during the time of application of the product 100′ about thenon-planar surface or at the location of the non-planar surface (i.e.,at a location different from where the product 100′ was manufactured,such as where the pipe is manufactured, or where the pipe is alreadyinstalled). For instance, in the event that the product 100′ isrelatively thin, such as a thickness between the first and second sides104, 108 not greater than about 5 mm (e.g., such as not greater thanabout 3 mm), the product 100′ may be conformed about a non-planarsurface (or into a desired non-planar shape) such as via hand or anyappropriate machinery.

As another example, and turning now to FIG. 7, one method 700 ofapplying a thermal insulation product (e.g., thermal insulation product100′) about a non-planar surface is disclosed. At 704, the method 700may include heating the thermal insulation product above a boiling pointof liquid within the product. For instance, the heating step 704 maycause at least some of the liquid within the product 100′ (e.g.,represented by the dashed lines in the bottom of the product 100′ inFIG. 2b ) to evaporate into a gaseous state (e.g., as shown in FIG. 2a )so as to render the product 100′ at least partially pliable orconformable (e.g., so as to render the product 100′ of FIG. 2b similarto the product 100 of FIG. 2a ). Before the heating step 704, theproduct 100′ may be substantially planar (e.g., as in FIG. 2b ) ornon-planar (e.g., such as in a concave or other shape), and may be at asubstantially evacuated pressures (e.g., not greater than about 20 mbarat a temperature of about 20° C.).

After the heating step 704, the method 700 may include conforming 708(e.g., wrapping) the inner surface of the thermal insulation product(e.g., second side 108 of product 100 of FIG. 2a ) to an outernon-planar surface (e.g., outer surface 404 of pipe 400). With referenceto FIG. 6, for instance, a first of the ends of the product 100 (nearseam 180) may be initially placed on or against the outer surface 404 ofthe pipe 400. Thereafter, the product 100 may be wrapped around at leasta portion of the outer surface 404 of the pipe 400 such as around amajority or even a substantial entirety of the outer surface 404 wherebythe second end of the product 100 may be placed adjacent the first endof the product. In one arrangement, the second side 108 (inner surface)of the product 100 may be appropriately secured to the outer surface 404of the pipe 400 and/or the first and second ends may be secured togetherat seam 180. Additionally or alternatively, the product 100 may be usedin conjunction with at least a second thermal insulation product 500 asdiscussed above. In the case where the thermal insulation product 100 isalready disposed against the inner surface 508 of the second thermalinsulation product 500, the heating step 704 may include heating both ofthe products 100′, 500 and then conforming both of the products 100, 500about the outer surface 404 of the pipe 400 (as in FIG. 6).

While the thermal insulation product is conformed to the non-planarsurface (or is otherwise in a desired non-planar shape or contour), thethermal insulation product may then be appropriately cooled 712 (e.g.,passively, actively) below the boiling point of the gas within theproduct. For instance, the cooling step 712 may cause at least some ofthe gas within the product 100 (e.g., represented by the small circlesand dashed lines dispersed throughout the product 100 in FIG. 2a ) tocondense back into the liquid state (e.g., as shown in the product 100′FIG. 2b ) so as to render the product 100 substantially rigid orunpliable (i.e., to rigidify the product in the non-planar shape) withthe interior portion of the product being in a low-pressure orsubstantially evacuated state (e.g., not greater than about 20 mbar at atemperature of about 20° C.). In one arrangement, the temperature of thefluid 600 may be below the boiling point of the liquid within theproduct 100.

In one arrangement, the gas-impermeable envelope 120 of the thermalinsulation product 100 may be appropriately constructed, treated ormanipulated so as to facilitate the ability of the product 100 to beshaped into a desired non-planar shape substantially free of tearing,rupture or breakage of the product 100. For instance, any appropriatesinusoidal shape, series of indentations, or the like may be formed intoone or both of the first and second sides 104, 108 (e.g., duringmanufacturing of the product, such as during the cooling process) tofacilitate bending or shaping of the product 100. As another example,some arrangements envisioned that the thickness of the gas-impermeableenvelope 120 may be higher on the one of the first or second sides 104,108 that is to be the outside surface when the product is formed into anon-planar shape (e.g., such as first side 104 in FIG. 6).

A further advantage of the finished/resulting thermal insulationproducts 100 disclosed herein will now be discussed. For instance,transient thermal performance of insulation products (e.g., the abilityto resist temperature equilibration between first and second sides of aninsulation product) can become important for applications in which the“hot” and “cold” temperatures respectively adjacent the opposing firstand second surfaces of the products are not temporally independent ofeach other (e.g., construction, refrigerated trucking, and/or the like).Stated differently, transient performance of an insulation productbecomes important when at least one of the first and second surfaces ofthe insulation product experiences temperature swings relative to theother surface.

Specifically, thermal diffusivity is a measure of transient performancegoverning the timescale for a material to equilibrate to a change inconditions and depends upon the thermal conductivity, density and heatcapacity of the material or product (where thermal diffusivity (α) isequal to the thermal conductivity (λ) divided by the density (ρ) andheat capacity (C_(p))). For instance, the characteristic time (i.e., forthe temperatures on the first and second surfaces of the product toequilibrate, where characteristic time increases with the square of theinsulation product thickness) for a 25 mm thick piece of ExpandedPolystyrene (EPS) foam insulation is on the order of a few minutes,while that of current VIPs is on the order of an hour or two. Generally,transient thermal performance increases with increasing characteristictime.

Before accounting for any phase changing effects of materials/componentsin the core of an insulation product (e.g., occurring during atemperature change adjacent a first side of an insulation productrelative to an opposing second side of the insulation product) ontransient performance of the insulation product, current VIPs and thepresent thermal insulation products 100 may have comparable transientperformance (e.g., both on the order of about an hour or two). However,the increased liquid (e.g., water) content of the present thermalinsulation products 100 (e.g., about 4 g/l) compared to that of currentVIPs (e.g., 0.5 g/l or less) may result in a greater degree of phasechanging of liquid into a vapor during temperature swings adjacent oneside of the products 100 and corresponding increased transientperformance of the present thermal insulation products 100 relative tocurrent VIPs.

For instance, assume that each of a current VIP and a present thermalinsulation product 100 is independently used as insulation for anoutside wall of a building. Assume that the building is always about 20°C. inside but swings between 5° C. outside at night (e.g., assume 12hours at 5° C. to idealize) and 35° C. outside during the day (e.g.,also assume 12 hours to idealize). In this case and without taking intoaccount phase changing effects of the liquid in the present thermalinsulation product 100 occurring during the temperature swings, about29.6 WHr/m² (106,560 J/m²) of heating and 29.6 WHr/m² (106,560 J/m²) ofcooling would be needed for one day for each of the current VIP andpresent thermal insulation product (e.g., assuming the characteristictime is much less than the 12 hour diurnal scales).

However, the phase changing of the liquid in the present thermalinsulation product 100 into vapor during the temperature swings on theoutside of the building serves to increase the transient performance ofthe product 100 by further cooling the first or second side of theproduct 100 during evaporation of the liquid depending upon which of thefirst and second sides is the “hot” side and which is the “cold” side.For instance, imagine that the first and second surfaces 104, 108 of thethermal insulation product 100 were respectively adjacent the inside andoutside of the building. Further assume that the outside of the buildingis initially at 5° C. and that the inside is at 20° C. In this case, therelatively lower 5° C. temperature outside of the building (e.g.,compared to the 20° C. temperature inside the building) may cause vaporwithin the product 100 to condense adjacent the second surface 108(e.g., as shown in FIG. 2b ).

However, as the second surface 108 of the product 100 heats owing to theoutside of the building increasing from 5° C. to 35° C. in this example,at least some of the liquid formerly condensed adjacent the secondsurface 108 on the inside of the product 100 evaporates (e.g., 100 g/m²)and subsequently condenses on the inside of the product 100 adjacent thefirst side 104 (e.g., as the inside of the building adjacent the firstside 104 is now colder (20° C.) than the outside of the buildingadjacent the second side (35° C.)). As the condensed liquid adjacent thesecond surface 108 of the product 100 absorbs energy (e.g., heat) fromthe second surface 108 to evaporate into a vapor, the net result is acooling effect adjacent the second surface 108 of the product 100 and acorresponding increase in transient thermal performance of the product100 (e.g., due to the aforementioned cooling effect tending to increasethe characteristic time of the product 100 or, in other words, the timeto temperature equilibrium between the first and second surfaces 104,108 of the product 100).

Once the outside begins cooling again (e.g., down to the 5° C.temperature), the above discussed process reverses whereby condensedliquid adjacent the first surface 104 of the product 100 evaporates andcondenses adjacent the second surface 108 of the product 100 (e.g. dueto the relatively hotter temperature (20° C.) inside the buildingrelative to outside the building (5° C.)) resulting in a cooling effectadjacent the first surface 104 of the product 100. In the event that thetime required to “pump” the fluid from the first surface 108 to thesecond surface 104 (and vice versa) approaches the diurnal timescales,transient thermal performance can be greatly increased in relation tocurrent VIPs.

EXAMPLE

A thermal insulation product is manufactured by way of disposing asupport material (including 90 wt. % fumed silica and 10 wt. % siliconcarbide) and steam at a temperature of about 100° C. within agas-permeable enclosure (Imperial RB1,product 39317 manufactured byHanes Engineered Materials) at ambient pressure, sealing the sealedgas-permeable enclosure within a gas-impermeable envelope (CryovakPFS8155 manufactured by the Sealed Air Corporation) at ambient pressureand with the steam maintained at the temperature of about 100° C., andthen cooling the gas-impermeable envelope (including the steamthereinside) for about 5 min down to a temperature of about 35° C.

After the temperature inside the gas-impermeable envelope drops down toabout 20° C., the pressure within the resulting thermal insulationproduct is about 8 mbar.

When measured with a cold side temperature of about 5° C. and a hot sidetemperature of about 25° C., the thermal conductivity of the thermalinsulation product is about 0.004 W/mK.

The bulk density of the thermal insulation product is about 140 g/l.

It is to be understood that the embodiments described above are forexemplary purposes only and are not intended to limit the scope of thepresent invention. Various adaptations, modifications and extensions ofthe described method will be apparent to those skilled in the art andare intended to be within the scope of the invention as defined by theclaims that follow.

What is claimed is:
 1. A thermal insulation product, comprising: a substantially gas-tight enclosure comprising first and second opposing surfaces and a thickness between the first and second opposing surfaces, wherein a ratio of the thickness to a radius of curvature of the first surface is at least about 1 to 8, and comprising first and second outer edge portions disposed along a length of the substantially gas-tight enclosure; a sealed interior portion within the substantially gas-tight enclosure between the first and second opposing surfaces and the first and second outer edge portions; a gas-permeable enclosure disposed within the substantially gas-tight enclosure; a support material comprising fine powder that is disposed within the gas-permeable enclosure; and a liquid within the sealed interior portion of the substantially gas-tight enclosure, wherein the pressure within the sealed interior portion is not greater than about 500 mbar at a temperature of at least about 20° C., wherein the substantially gas-tight enclosure comprises a substantially gas impermeable envelope comprising at least one of a polymeric film and a metallic foil.
 2. The product of claim 1, wherein the ratio of the thickness of the substantially gas-tight enclosure to the radius of curvature of the first surface is at least about 1to
 4. 3. The product of claim 1, wherein the ratio of the thickness of the substantially gas-tight enclosure to the radius of curvature of the first surface is at least about 1 to
 2. 4. The product of claim 1, wherein the first surface of the substantially gas-tight enclosure is at least partially cylindrically-shaped.
 5. The product of claim 1, wherein the first surface of the substantially gas-tight enclosure is substantially cylindrically-shaped.
 6. The product of claim 1, wherein the thickness of the substantially gas-tight enclosure is at least about 2 mm.
 7. The product of claim 1, wherein the thickness of the substantially gas-tight enclosure is at least about 10 mm.
 8. The product of claim 1, wherein the thickness of the substantially gas-tight enclosure is at least about 20 mm.
 9. The product of claim 1, wherein the thickness of the substantially gas-tight enclosure is not greater than about 80 mm.
 10. The product of claim 1, wherein the thickness of the substantially gas-tight enclosure is not greater than about 60 mm.
 11. The product of claim 1, wherein the radius of curvature of the first surface is at least about 3 mm.
 12. The product of claim 1, wherein the radius of curvature of the first surface is not greater than about 6 mm.
 13. The product of claim 1, wherein the fine powder is selected from at least one of silica powder and an aerogel powder.
 14. The product of claim 13, wherein the fine powder comprises fumed silica.
 15. The product of claim 1, wherein the support material comprises at least about 60 wt % of the fine powder.
 16. The product of claim 1, wherein the support material comprises about 100 wt % of the fine powder.
 17. The product of claim 1, wherein the substantially gas impermeable envelope comprises an Ethylene Vinyl Alcohol (EVOH) barrier film.
 18. The product of claim 1, wherein the substantially gas impermeable envelope comprises a coextruded polyethylene (PE)/EVOH barrier film.
 19. The product of claim 1, wherein the substantially gas impermeable envelope comprises a metallized EVOH barrier film.
 20. The product of claim 1, wherein the sealed interior portion comprises at least about 2 grams of the liquid per liter of a total volume of the sealed interior portion.
 21. The product of claim 1, wherein the sealed interior portion comprises at least about 4 grams of the liquid per liter of a total volume of the sealed interior portion.
 22. The product of claim 1, wherein the liquid comprises at least one component selected from the group consisting of water, paraffins, chlorohydrocarbons, chlorofluorocarbons, and oxygenated organics.
 23. The product of claim 22, wherein the liquid comprises water.
 24. The product of claim 1, wherein the first and second outer edge portions are in contact along the length of the enclosure.
 25. The product of claim 1, wherein the substantially gas-impermeable envelope comprises a metallized plastic.
 26. The product of claim 25, wherein the substantially gas-impermeable envelope comprises metallized polyethylene terephthalate.
 27. The product of claim 1, wherein the substantially gas-impermeable envelope has a thickness of at least about 10 microns and not greater than about 300 microns. 